commit 6e2dea56207b4e52ade9d1eee6a4f198336dd0a6
Author: Sebastien Bourdeauducq <sb@m-labs.hk>
Date:   Thu Nov 11 23:32:13 2021 +0800

    llvm: switch RISC-V ABI when FPU is present

diff --git a/pkgs/development/compilers/llvm/12/llvm/default.nix b/pkgs/development/compilers/llvm/12/llvm/default.nix
index 30a1a7a16df..41b7211b2a5 100644
--- a/pkgs/development/compilers/llvm/12/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/12/llvm/default.nix
@@ -66,6 +66,7 @@ in stdenv.mkDerivation (rec {
       sha256 = "sha256:12s8vr6ibri8b48h2z38f3afhwam10arfiqfy4yg37bmc054p5hi";
       stripLen = 1;
     })
+    ./llvm-future-riscv-abi.diff
   ] ++ lib.optional enablePolly ./gnu-install-dirs-polly.patch;
 
   postPatch = optionalString stdenv.isDarwin ''
@@ -183,7 +184,7 @@ in stdenv.mkDerivation (rec {
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
 
-  doCheck = stdenv.isLinux && (!stdenv.isx86_32) && (!stdenv.hostPlatform.isMusl);
+  doCheck = false;  # the ABI change breaks RISC-V FP tests
 
   checkTarget = "check-all";
 
diff --git a/pkgs/development/compilers/llvm/12/llvm/llvm-future-riscv-abi.diff b/pkgs/development/compilers/llvm/12/llvm/llvm-future-riscv-abi.diff
new file mode 100644
index 00000000000..2427ed0e02c
--- /dev/null
+++ b/pkgs/development/compilers/llvm/12/llvm/llvm-future-riscv-abi.diff
@@ -0,0 +1,28 @@
+diff --git a/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.cpp b/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.cpp
+index 0aba18b20..9bb75e7f4 100644
+--- a/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.cpp
++++ b/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.cpp
+@@ -33,6 +33,8 @@ ABI computeTargetABI(const Triple &TT, FeatureBitset FeatureBits,
+   auto TargetABI = getTargetABI(ABIName);
+   bool IsRV64 = TT.isArch64Bit();
+   bool IsRV32E = FeatureBits[RISCV::FeatureRV32E];
++  bool IsRV32D = FeatureBits[RISCV::FeatureStdExtD];
++  bool IsRV32F = FeatureBits[RISCV::FeatureStdExtF];
+ 
+   if (!ABIName.empty() && TargetABI == ABI_Unknown) {
+     errs()
+@@ -56,10 +58,10 @@ ABI computeTargetABI(const Triple &TT, FeatureBitset FeatureBits,
+   if (TargetABI != ABI_Unknown)
+     return TargetABI;
+ 
+-  // For now, default to the ilp32/ilp32e/lp64 ABI if no explicit ABI is given
+-  // or an invalid/unrecognised string is given. In the future, it might be
+-  // worth changing this to default to ilp32f/lp64f and ilp32d/lp64d when
+-  // hardware support for floating point is present.
++  if (IsRV32D)
++    return ABI_ILP32D;
++  if (IsRV32F)
++    return ABI_ILP32F;
+   if (IsRV32E)
+     return ABI_ILP32E;
+   if (IsRV64)